1. Field of the Invention
This invention relates to a catalyst useful for the production of a gaseous mixture containing hydrogen as a principal ingredient, by the steam reforming of hydrocarbons.
The catalyst of the present invention makes it possible to use, in the steam reforming process, heavier hydrocarbons such as kerosene and gas oil which cannot be used in the presence of a conventional catalyst. Such heavier hydrocarbons can be steam-reformed into hydrogen-rich gaseous mixtures stably and continuously for a long period of time. In addition the catalyst of the invention is also useful with light hydrocarbon feedstocks such as natural gas, ethane, propane, butane and straight-run naphtha.
2. Description of the Prior Art
Nickel catalysts have been used widely as steam reforming catalysts. However, it has been well known that the nickel catalysts are deactivated rapidly by sulfur contained in the feed hydrocarbons and, therefore, pretreatment of the feedstock hydrocarbons for removing a major portion of sulfur therefrom is critical. Usually, the allowable sulfur impurity content is limited to a low level, such as 0.2 ppm.
Further, depending on the kind of feedstock hydrocarbons and/or reaction conditions, thermal cracking of the hydrocarbons may proceed excessively due to the high activity of nickel and the carbon thus formed is deposited on the catalyst surface to block the catalyst from the reactants, thereby inhibiting the steam reforming reaction. As a result, an inactive catalyst is present in the reaction zone so that only the thermal cracking of the hydrocarbons proceeds whereby carbon accumulates rapidly in the reaction zone. Thus, the space in the reaction zone becomes filled with carbon in a short period of time.
Thus, in the prior art, a highly effective desulfurization treatment of the feedstock hydrocarbons is necessary. Also, the deposition of carbon on the catalyst surface is a fatal barrier to a continuous catalytic gasification process.
Accordingly, for preventing deposition of carbon formed by the reaction on the surface of the nickel catalyst, reduction of the high activity of nickel has been considered and incorporation of a compound of a metal such as potassium in the catalyst composition has been effected in practice. However, such a means is ineffective for heavy hydrocarbon feedstocks, although it may be effective for light hydrocarbon feedstocks.
The improvement caused by the addition of potassium or the like to the nickel catalyst, however, involves some problems such as an excessive reduction of the intrinsic activity of nickel, deterioration of the catalyst due to vaporization of the additives and adherence of the evaporated substances to lower temperature parts of the apparatus.
A process for preparing nickel-free catalysts effective for steam reforming, catalytic partial oxidation and catalytic thermal cracking is described in U.S. Pat. No. 3,969,542.
The catalysts disclosed in U.S. Pat. No. 3,969,542 are nickel-free, firm, sintered products obtained from alkaline earth metal oxides and aluminum oxide by a specified method. They have a remarkable sulfur resistance and a carbon deposition-preventing property and, further, they are free from the problem caused by vaporization of catalyst ingredients.
For further improving the catalysts of U.S. Pat. No. 3,969,542 to increase the activity thereof, the inventors investigated catalyst additives, repeatedly made experiments by using various additives and determined the results thereof.